1. Field of the Invention
The present invention relates to a method for producing an orientational ceramic, an orientational ceramic, and a ceramic electronic component, and more particularly, relates to a method for producing an orientational ceramic which has a crystalline orientation, an orientational ceramic produced with the use of this production method, and a ceramic electronic component such as a piezoelectric ceramic electronic component and a dielectric ceramic electronic component using this orientational ceramic.
2. Description of the Related Art
Various electronic devices nowadays have ceramic electronic components mounted therein, and in these ceramic electronic components, ceramic sintered bodies which contain a ceramic material as their main constituent are widely used.
In addition, composite oxides which have a perovskite-type crystalline structure (hereinafter, referred to as “perovskite-type compounds”) such as barium titanate and lead zirconate titanate (hereinafter, referred to as a “PZT”) have been widely used as ceramic materials for use in dielectric bodies and piezoelectric bodies.
This type of ceramic sintered body is known to have various types of properties such as piezoelectric properties and dielectric properties which are improved by controlling the orientation of crystals. For example, tetragonal PZT is known to exhibit excellent piezoelectric properties or ferroelectric properties by achieving a c-axis orientation parallel to the polarization axis.
Furthermore, for example, Patent Documents 1 to 4 below are known as prior art which relates to an orientational ceramic sintered body.
Patent Document 1 proposes a method for producing an orientational ceramic sintered body in such a way that which a non-ferromagnetic powder that has a non-isometric crystalline structure is dispersed in a solvent, and the resulting slurry is subjected to forming by solidification in a magnetic field, and then subjected to sintering.
In Patent Document 1, for example, a slurry is prepared by dispersing an anisotropic substance such as alumina in an aqueous solution with an appropriate amount of polyelectrolyte added thereto, subjected to casting in which the slurry is cast into a porous mold and subjected to forming in a magnetic field, and then subjected to firing to obtain an orientational ceramic (sintered body).
Patent Document 2 proposes a method for producing an orientational ceramic, which includes the steps of: obtaining a ceramic slurry containing a polycrystalline ceramic powder; obtaining a ceramic compact by subjecting the ceramic slurry to forming in a magnetic field; and firing the ceramic compact, where the polycrystalline ceramic powder contains a main constituent composed of a perovskite-type compound and a predetermined amount of accessory constituent, and the accessory constituent is at least one Group III transition metal ions with a non-zero magnetic moment and rare-earth transition metal ions with a non-zero magnetic moment.
Also in Patent Document 2, a ceramic raw material powder is dispersed in an appropriate amount of water to prepare ceramic slurry, and then, as in Patent Document 1, the slurry is subjected to casting in a magnetic field, and then firing to obtain an orientational ceramic.
Further, the use of the polycrystalline ceramic powder containing the accessory constituent in a predetermined amount with respect to the main constituent of the perovskite-type compound such as barium titanate in Patent Document 2 allows an orientation in a magnetic field even in the case of using a polycrystalline ceramic powder.
Patent Document 3 proposes a method for manufacturing a piezoelectric ceramic component in which the step of preparing ceramic green sheets includes the steps of: applying a ceramic slurry containing non-magnetic ceramic particles and an ultraviolet curable binder onto base films to obtain non-oriented sheets with a predetermined thickness; feeding the non-oriented sheets into a magnetic field application system while the non-oriented sheets is supported by the base films, and applying a magnetic field in a predetermined direction to orient the non-magnetic ceramic particles in the non-oriented sheets in the direction of the magnetic field, thereby providing oriented sheets; and fixing the orientation of at least some of the non-magnetic ceramic particles in the oriented sheets.
In Patent Document 3, a bismuth layered compound or a tungsten bronze-type compound is used for the non-magnetic ceramic particles, a polyvinyl butyral resin, a cellulose resin, an acrylic resin, or the like is used for the binder resin, the ceramic slurry containing the non-magnetic ceramic particles and the binder resin is used to prepare non-oriented sheets, and the non-oriented sheets are oriented by applying a magnetic field thereto.
Furthermore, oriented sheets which have uniform particle orientation achieved by the application of the magnetic field in Patent Document 3 are prepared by making the non-oriented sheets on the base films uniform in thickness, and the oriented sheets are cured by ultraviolet irradiation, so that oriented sheets are thereby obtained which have predetermined particle orientation.
Patent Document 4 proposes a method for producing a sintered body of a perovskite-structure compound, which includes the steps of: preparing a single-crystalline powder of a perovskite-type compound; preparing, as a dispersion phase, a ceramic slurry containing the single-crystalline powder; obtaining a ceramic compact by shaping the ceramic slurry in a magnetic field; and sintering the ceramic compact.
In Patent Document 4, a single-crystalline lead titanate (hereinafter, referred to as “PT”) as the perovskite-type compound is used as a ceramic raw material powder, and a ceramic slurry containing the ceramic raw material powder and a polyvinyl alcohol resin as a binder resin is shaped in a magnetic field to prepare a ceramic compact, so as to obtain an orientational ceramic (sintered body) with a high degree of orientation.